1. Field of the Invention
The present invention relates to dyeing of fibers and more particularly to reactively dyed fibers in which a chromophore is linked through a condensation residue to sites on the fiber.
2. Description of the Prior Art
Dyes are retained in fibers by physical adsorption, salt or metal-complex formation, solution, mechanical retention, or the formation of covalent chemical bonds. Physical adsorption and solution, in which the dye is partitioned between the fiber and the surrounding aqueous phase, are equilibrium reactions, and only by very careful selection of the dyes used, can good washfastness properties be achieved. Salt and metal complex formation are also equilibrium reactions and, though generally the retention of the dye is favored more than in physical adsorption, washfastness may still present a problem. The dyes that are held by mechanical retention (azoics, vats and sulfurs) are virtually insoluble in water and shown excellent fastness to washing, but have other disadvantages. They are, for example, difficult and expensive to apply; loose dye, which is not easily washed off, may be deposited on the surface, resulting in low fastness to rubbing (crockfastness), and the final shade of the dyeing does not develop until completion of the whole dyeing cycle and aftertreatments.
Chemical bonding of dye to fiber for fixation of dye was recognized as early as 1895. The reactive dye systems presently available require that the dyes contain a functional group capable of forming a covalent chemical bond with the fiber.
Fiber-reactive dyes are employed quite widely in coloring cellulosics and proteinaceous fibers. They, of course, exhibit excellent washfastness, resistance to rubbing, tinctorial powers, ease of application and leveling. The latter quality is a measure of uniformity and most important for long dye runs and color matching. The reaction of the dye with cellulosic fibers is basically an esterification or etherification reaction and is broadly represented as: ##STR1##
The triazine reactive group imparts oil solubility characteristics to the high molecular weight dye which hinder and interfere with an aqueous solubilizing group such as --SO.sub.3 H. These dyes are unstable and difficult to work with. Most of the reactive dye systems are based upon chemistry where the reaction is effected in alkaline solutions. There are few present reactive dye systems which operate effectively at an acid pH. Such a system is desirable in the dyeing of mixed fabrics such as cotton blends with polyester, wool or nylon.
The American Cyanamid Company has published a booklet entitled "Cyanamide", which sets forth a considerable number of reactions of cyanamide and dicyandiamide. Page 32 of this booklet indicates that cyanamide was long known to be a dehydrating agent when warmed with anhydrous formic acid and in the esterification of lactic or salicylic acid in absolute ethanol. Note Pratorius-Seidler; G., J. prakt. Chem. [2] 21, 129-50 (1880); C. 1880, 245. A number of papers have investigated the reaction of cyanamide with carboxylic acids, and have proposed a mechanism wherein the acid is converted to the anhydride by interaction with cyanamide, with formation of urea, followed by acylation of the urea by the anhydride to produce a ureide, which at elevated temperatures interacts with the acid to produce an amide. Cyanamide and dialkylcyanamides are also useful in the synthesis of pyrophosphates. Kenner, G. W., Reese, C. B., and Todd, A. R., J. Chem. Soc. 1958, 546-51; C.A. 52, 11072 (1958) indicates that a high energy phosphorus-oxygen bond is present in the presumed intermediate O-phosphorylpseudourea.
The use of cyanamide and phosphoric acid to impart flame retardant properties to cotton and other cellulosic fabrics is well known to the art. For instance, O'Brien, "Cyanamide Based Durable Flame-Retardant Finish for Cotton", Textile Research Journal, March, 1968, pp. 256-266 indicates, at page 265, that the reaction of cyanamide and phosphoric acid with cellulose results in a cross-linking of cellulose molecules. From the properties of the resulting product, it is suggested that the cross-linked cellulose is some type of dicellulose phosphate ester.